This invention relates to a mobile telephone apparatus and, more particularly, to a mobile telephone apparatus for connecting a portable telephone terminal to a vehicle-mounted booster device and performing communication via a vehicle-mounted antenna.
In a mobile phone system of the cellular type, as shown in FIG. 7, a service region is subdivided into a number of cells (wireless zones) 1.sub.1, 1.sub.2, 1.sub.3, . . . , and the cells are provided with individual wireless base stations 2.sub.1, 2.sub.2, 2.sub.3, . . . , respectively. The wireless base stations are formed into groups each having several of the base stations, a wireless line-control station (not shown) is provided for each such group of wireless base stations, the wireless line-control stations are connected to a mobile phone exchange (hereinafter referred to as a car phone exchange) 3, and the car phone exchange 3 is connected to an exchange 4 of a public telephone network. The cellular-type mobile phone system is so designed that as a portable telephone terminal 5 or car telephone terminal 6 moves, the wireless base stations that send and receive the radio waves are changed over from one to another so that communication can be achieved with an indoor fixed telephone 7 or another mobile telephone terminal. This makes it possible to carry on telephone conversations over a wide area and to increase the number of channels. The number of lines can be increased without limit as well.
When power is supplied to the mobile telephone terminals 5 and 6, the terminals scan the paging channels of the surrounding wireless base stations, receive the paging waves transmitted at all times from each wireless base station and tune to the channel of the station having the strongest signal. Thereafter, the terminals receive position information over this channel and compare this with position information already stored. If the two items of position information differ, each terminal sends an ID code, which has been stored in a ROM, to the wireless base station over the paging channel and registers position with the car phone exchange 3. As a result, the mobile telephone terminal enters a waiting mode. When the mobile telephone terminal moves and the strength of the received signal weakens, the terminal performs scanning again. In this way wireless base stations are changed over in successive fashion
When an outgoing call is placed, the calling party enters the other party's telephone number from a control panel and presses a transmission key, whereupon the mobile telephone terminal sends its ID code and the called party's telephone number to the wireless base station over the paging channel and the wireless base station responds by transmitting the received information to the wireless line-control station (not shown). The latter decides the speech channel, notifies the mobile telephone terminal via the wireless base station and informs the car phone exchange 3 of the outgoing-call information and speech channel that has been decided. The car phone exchange 3 checks to determine whether the ID code contained in the call information received has been registered and, if the ID code has, connects the speech channel to the public telephone system. The mobile telephone terminal can then communicate with the called party's terminal via the designated speech channel.
During a telephone conversation, the reception field strength is checked. When the reception field strength weakens and falls below a set level, the wireless base station is changed over. More specifically, the speech channel is changed over to perform hand-off. In addition, the transmitting power of the mobile terminal is controlled in accordance with a command from the wireless base station. In automatic power control (APC) of transmitting power, when sensitivity improves as the mobile telephone terminal approaches the wireless base station, transmitting power is reduced by a command from the base station. Conversely, when sensitivity diminishes as the mobile telephone terminal becomes more distant from the wireless base station, transmitting power is raised in accordance with a command from the base station. In accordance with APC, transmitting power is capable of being variably controlled over eight stages of 4 dB each. Consumption of battery power can be suppressed by suppressing the transmitting power when sensitivity is high (i.e, when field strength is high). Conversely, by increasing transmitting power when field strength is low, the area reached by the radio waves is enlarged so that frequent changeover (hand-off) of the speech channel does not occur and there is less deterioration in voice quality. Since there is a momentary interruption in sound at the time of hand-off, this makes conversing unpleasant. Voice quality deteriorates when hand-off takes place frequently.
In view of this deterioration in voice quality caused by hand-off, maximum transmitting power of a portable telephone terminal should be enlarged. In order to raise transmitting power, however, the battery or antenna must be enlarged. This results in a larger apparatus, which is more difficult to carry about. For this reason, the specifications of a portable telephone terminal are a voltage of 6 V and a maximum transmitting power of 6 W in order to provide a terminal that is easy to carry.
It should be noted that even if transmitting power is reduced and the area covered by the radio waves contracts as a result, walking about while carrying on a telephone conversation using the portable telephone terminal does not pose a problem since the traveling speed is low and there is almost no hand-off of the channel.
However, in a case where the portable telephone terminal is taken into an automotive vehicle and is used for a call while the vehicle is traveling, the high traveling speed of the vehicle results in frequent hand-off, which invites a decline in sound quality. Accordingly, a booster device is installed within the vehicle and the portable telephone terminal is connected to the booster device when a telephone call is made from within the vehicle. The party using the portable telephone terminal communicates with another party via the antenna mounted on the vehicle.
FIG. 8 is a block diagram for describing a mobile telephone apparatus obtained by connecting a portable telephone terminal to a booster device. Shown in FIG. 8 are a portable telephone terminal 11, a terminal installing rack 12 provided in the vicinity of the driver of the vehicle, a booster device 13 provided in the trunk of the vehicle, an antenna 14 of the portable telephone terminal, a telephone antenna 15 mounted on the vehicle, a battery 16 mounted on the vehicle, and an ignition switch 17.
The portable telephone terminal 11 and the terminal installation rack 12 are suitably connected by a cord 18 provided on the installation rack 12, and the terminal installation rack 12 and booster device 13 are connected beforehand by a coaxial cable 19a and a power-supply line 19b. A voltage of 13.8 V from the vehicle-mounted battery 16 is supplied to a high-frequency circuit in the booster device 13 and a voltage regulator 12a in the terminal installation rack 12, the voltage is converted from 13.8 V to 6 V by the voltage regulator 12a, and the voltage of 6 V is applied to the portable telephone terminal 11. The voltage regulator 12a has the construction of a DC-DC converter, such as the construction illustrated in FIG. 9. As shown in FIG. 9, the voltage regulator 12a includes a chopper 12a-1 for chopping the DC voltage of 13.8 V at a prescribed frequency, a transformer 12a-2 capable of regulating output voltage, a rectifier 12a-3 and a constant-voltage circuit 12a-4 for outputting a constant voltage (=6 V).
The portable telephone terminal 11 and a duplexer 13a on the terminal side of the booster device 13 are connected by a coaxial cable 19a, and high-frequency amplifiers 13c, 13d for transmission and reception, respectively, are provided between the duplexer 13a and a duplexer 13b on the antenna side. The booster 13 is supplied with the voltage of 13.8 V from the vehicle-mounted battery 16 and is capable of outputting a maximum transmitting power of 3 W.
The transmitting section of the portable telephone terminal 11 applies high-frequency power amplification to a high-frequency signal obtained by frequency modulating a voice signal or data, and the amplified signal is applied to the transmitting high-frequency amplifier 13c of the booster device 13 via the coaxial cable 19a. The transmitting high-frequency amplifier 13c of the booster device 13 subjects the high-frequency signal entering from the portable telephone terminal 11 to further high-frequency power amplification so as to boost the transmitting power, which is then emitted from the antenna 15.
A signal received by the antenna 15 is subjected to high-frequency power amplification by the receiving high-frequency amplifier 13d of the booster device 13, after which the amplified signal is applied to the receiving section of the portable telephone terminal via the coaxial cable 19a so as to be demodulated to the original voice signal or data. The portable telephone terminal 11 performs transmission-power control and, in accordance with a command from a wireless base station, exercises control so as to vary the transmitting power of the high-frequency amplifier over eight stages from the minimum level to the maximum level (=0.6 W).
Thus, as set forth above, the booster device 13, which is supplied with a voltage of 13.8 V from the vehicle-mounted battery 16, is capable of outputting a maximum transmitting power of 3 W. As a result, the area covered by the radio waves is enlarged so that frequent hand-off will not occur even at a high traveling speed. This makes it possible to eliminate a deterioration in sound quality.
It should be noted that it is necessary to output a maximum transmitting power of 6 W even in a state in which the portable telephone terminal 11 is connected to the booster device 13. This means that the voltage regulator 12a provided on the terminal installation rack 12 must be capable of supplying a power of 6 W. This is a problem in that the rated capacity of each component is large, thereby increasing size and raising cost. In particular, since the space available within the vehicle compartment is limited, it is required that the terminal installation rack be made as small as possible. However, since the voltage regulator is large in size in the prior art, this is an impediment to reducing the size of the terminal installation rack.